Pressure sensitive diaphragms with stress null zone oriented bridge patterns



C. K. STEDMAN PRESSURE SENSITIVE DIAPHRAGMS WITH STRESS NULL ZONEORIENTED BRIDGE PATTERNS 5 Sheets-Sheet 1 Filed Aug. 25, 1961 5 M H w Hm 9 8 7 6 5 4 5 2 fl O 4 Q 1 4 6 o 4 3 we aw L2 ML m a v m n l 8 0n (\I7 a I ny/ w/ 6 D Y AW M M; W 5 m n mm 4 fl m rz v 7 S 1 4. HEM n RD: S I3 a r-AM B 0 A R U l F J fl 2 w l M B m u m 9 8 7 6 5 4 3 2 H o. 4 4 4 wi 4 6M INVEN TOR. 060/; A. .S'ffDMA/V Wm M W Filed Aug. 25, 1961 Jan. 1,1963 3,071,745

C. K. STEDMAN PRESSURE SENSITIVE DIAPH GMS WITH STRESS NULL ZONEORIENTED BR E PATTERNS 5 Sheets-Sheet 2 24 I 22 I y l 30 36k :04,INVENTOR.

c'A-d/L x. SIEMAIV v I I I 811 mm Trot/V1945 Jan. 1', 1963 F l d A g 251961 3,071,745 TH STRESS TERNS 5 Sheets-Sheet 5 INVENTOR. 050/4 A.S'I'EDM/M/ N (In; AW ,4 I'I'OEA/EVJ' C. K. STEDMAN PRESSURE SENSITIVEDIAPHRAGMS WI NULL ZONE ORIENTED BRIDGE PAT Jan. 1, 1963 K. STEDMAN 3,07

C. PRESSURE SENSIT E DIAPHRAGMS W STRESS NULL ZONE OR TED BRIDGE PA RNSFiled Aug. 25, 1961 5 Sheets-Sheet 4 r I I 3 45 /1 (0 40 1o 26 Z2 36 6O26 VENTOR. 050/4 s'repmm/ 1963 c K STEDMAN 3,071,745

PRESSURE SENSI TIV E DIAPHRAGMS WITH STRES NULL ZONE ORIENTED BRIDGEPATTERNS Flled Aug- 25, 1961 5 Sheets-Sheet 5 I50 v\\\\ I /30 BYCWWA AWA I'TORN'Yd' United States Patent PRESSURE SENSITfVE DIAPHRAGMS WITHSTRESS NULL ZONE ORIENTED BRIDGE PATTERNS Cecil K. Stedman, Enumclaw,Wash., assignor to Statham Instruments, Inc., Los An eles, Calif., acorporation of California Filed Aug. 25, 1961, Ser. No. 134,070 41Claims. (Cl. 3382)' The present invention relates to pressure sensitiveassemblies, also known as transducers, of the type in which thetransduction means comprises a bridge pattern in the form of an integralfilm or the like bonded to a flexible diaphragm, with strain sensitivechange in electrical resistance of the active segments of the bridgepattern providing an indication of magnitude of pressure exerted on thediaphragm. I

More particularly, the present invention relates to pressure responsivetransducer assemblies employing a flexible diaphragm having thereon abonded bridge pattern in the form of an integral film or the like;wherein the bridge pattern comprises a plurality of active segmentsinterconnected at juncture areas in turn having relatively lowresistance conductor segments extending beyond the restrained edge ofthe diaphragm, the arrangement of said pattern being such that each ofsaid juncture areas 1 lies substantially in the radial stress null zoneof the diaphragm, with one active segment connected to each juncturearea disposed near-center from said null zone and with the other activesegment connected to said juncture area disposed near-edge from saidnull zone, and wherein such near-edge active segment is advantageouslydisposed so that a major part thereof is in the area of and outside thetangential stress null zone of said diaphragm. In certain preferredforms of the bridge pattern the active segments thereof are composed ofan electroconductive material having a substantial transverse gagefactor (G and the active segments are oriented to advantageously utilizesuch transverse gage factor and thereby increase bridge sensitivity, thearrangement of such near-edge active segment being with a substantialpart thereof disposed outside of the tangential stress null zone of thediaphragm and extending parallel to the restrained edge thereof, so thatthe bridge material in substantial part responds to radial stress inrelation to its transverse gage factor and in substantial part respondsto tangential stress in relation to its parallel gage factor with suchresponses augmenting each other.

In certain of its aspects, other advantages and characteristics of theinvention pertain to simple, durable and reliable arrangements of thebridge pattern to integrally include conductor film or like segments inturn having conductor output leads connected thereto, the pressuresensitive diaphragm of the assembly having a backing plate bondedthereto near the edge of the diaphragm, the conductor segments extendingfrom the active segments to annularly oriented positions externally ofthe backing plate, such conductor output leads being attached as bysoldering to the conductor segments, with the junctions beingencapsulated in means bonding the diaphragm and backing plate together,

Other aspects of the present invention involve the presentation ofseveral modified forms and variations of .bridge patterns characteristicof the invention, and techniques for fabricating the bridge films, aswell as techniques for assembling transducer assemblies comprising suchbridge films. Specific aspects of the invention also pertain to suitableelectroconductive materials and suitable orientation of active bridgesegments on a diaphragm in order to realize to greatest advantage theincrease in 3,071,745 Patented Jan. 1, 1963 sensitivity resulting fromthe transverse gage factors characteristic of certain materials.

As used herein, the terms active segments and active film segments referto those portions of the bridge film pattern comprising the socalledarms or legs of an electrical bridge, which reflect substantial changein electrical resistance responsive to change in stress, i.e. thosesegments which are resistively active in performing the measuringfunction of the device. By the terms conductor segments and conductorfilm segments are meant those relatively low resistance segments of thebridge pattern connectively associated with the active segmentsinternally of the assembly and terminating externally of the diaphragm,serving as input and output connection points or juncture areas for theactive segments. By the terms conductor output leads and output leadsare meant the wire or like means connected to such conductor filmsegments externally of the diaphragm and lead externally of theassembly, by means of which leads the voltage input and variable outputof the active segments are electrically transmitted to externallyassociated measuring equipment.

By the term parallel gage factor, or G is meant the sensitivity of thefilm or like material to change in electrical resistance resulting fromthe stress or component stress exerted parallel to or in the directionof current flow. By the term transverse gage factor, or 6,, is meant thesensitivity of the bridge material to change in electrical resistanceresulting from the stress or component of stress exerted perpendicularlyor transversely to the direction of current flow.

By the term radial stress null zone is meant the annular zone of thediaphragm in which no substantial radial stress occurs upon fiexure ofthe diaphragm, i.e. the zone wherein the factor of magnitude than thedimension of the diaphragm. By

the terms integral film" and integrally formed film, .are meant a filmof homogeneous nature throughout, comprising no soldered or likediscrete connection of separately formed segments.

As is known, when an edge restrained flexible diaphragm is subjected todifferential pressure at the faces,

the diaphragm is loaded to be in compression in certain areas anddirections and to be in tension in other areas Compound stresses occursuch that portions of the diaphragm are under substantial radial and/ ortangential tensile stress and other portions of the, diaphragm are undersubstantial radial and/ or tangential compression stress. By the termsradial stress or 8,, and relative radial stress, or S,, are meant thephysical stresses exerted on the diaphragm and bridge pattern which areexerted in a direction radially of the center of the diaphragm. By theterms tangential stress, or S and relative tangential stress, or aremeant stresses exerted in a direction parallel to the restrained edge ofthe diaphragm. Considering the stresses as they occur in relation to thecenter and restrained edge of the diaphragm, a given condition ofloading and diaphragm flexure causes either compression or tensionstress relatively near the center of the diaphragm and either tension orcompression stress relatively near the edge of the diaphragm, dependingupon the direction of fiexure. The hereinafter discussed considerations,as-tothe relation of stresses exerted in various regions of thediaphragm expressed in terms of the distance/radius (r/a) ratio,

assuming for simplicity that the direction of fiexure is toward the sideof the diaphragm on which the bridge -film.pattern is.arranged,i.e.assuming the'condition where the bridge in its near-center regions isunder tension and in its near-edge regions is undercompression, with thetensile stresses being denoted negative and the -compression stressesbeing denoted positive. However, as 'will be apparent, the principleshere involved are equally applicable to the converse situation where thebridge in its near-center regions is under compression and in its bridgeis internally self-balancing, are basic objects and features of theinvention.

The bridge segments are integrally formed as by vapor deposition, to bethe same composition and thickness throughout so that all portionsthereof have the same responsiveness to temperature changes andto aging.Preferably, each active bridge segment has about the same length/widthratio as the other active segment or segments, to be internally balancedwith electrically equal bridge arms. Also, each active film segment hasa substantial area and is as long as practicable, consistent with otherdesign factors, in order that the heat generated in the segment bedissipated ,over a substantial area. At

least two and preferably four active segments are employed, one segmentor opposed pair of segments being relatively near the'center of thediaphragm and the other segment or opposed pair of segments beingrelatively close to the restrained edge of the diaphragm so that onesegment or pair is under compression while the other segment or pair isunder tension. However, use of four active segments is preferable formaximum sensitivity, with one opposed pair positioned on tensionedregions of the diaphragm and the other opposed pair positioned incompressed regions of the diaphragm, so as ,to provide a line pattern inthe form of a loop in which all the segments electrically augment eachother when connected as a Wheatstone bridge.

In such an arrangement involving four active film segments, thesegmentsare quadrantly related, with one opposite pair of the segments disposedsymmetrically of each other soas to be subjected to substantially thesame stresses, while the other opposite pair is likewise symmetricallyoriented with respect to each other soas to be also subjected tosubstantially the same 7 stresses. In order to minimize internal heatingeffects, and consistent with the foregoing considerations, it is anothercharacteristic of the film bridge patterns of the present invention thatthe active segments are each spread .over a substantial area (i.e. as afilm), yet are spaced a substantial distance from each other.

In preferred forms of the bridge film pattern as herein disclosed, thearrangement of active segments comprises .two oppositely disposed activesegments situated near the .center of the diaphragm and two oppositelydisposed active segments situated near the restrainededge of thediaphragm, in conjunction with integrally formed, rela- .tively lowresistance conductor segments, all of similar configuration andorientation on the diaphragm. This is accomplished most practicably bymaking the active segments and conductor segments of'the same materialand same thickness. This integration of the conductor segments withthe'active segments serves the advantage of eliminating any necessityfor separate output lead connections within the restrained edge of thediaphragm, with consequent constructional simplification. Suchconstructional simplification also avoids the problem of internalconnections being a limiting factor in the minimum size capability ofthe transducer. The integration of active and conductor segments alsoavoids the sometimes troublesome problem of bridge balance variationscaused by the presence of soldered'connections at the bridge armterminals.

Twoopposed conductor segments serve to transmit the voltage input to thebridge loop, and the other two opposed conductor segments serve totransmit the bridge output voltageor signal to the output leads.

Still other features and advantages characteristic of the presentinvention include the utilization of abridge V film pattern formed toinclude integral, low resistance conductor segments extending to theperiphery of the diaphragm, :with the film conductor segments bonded tothe diaphragm and with the backing plate also bonded to the diaphragm,and with the bonding means between the periphery of the diaphragm andthe outer portion of the backing plate serving to encapsulate leadconnections to saidconductor film segments, such manner of constructionand assembly providing that the assembly is constructionally rugged andelectrically insulated.

The bridge pattern mounting diaphragm is preferably but not necessarilycircular in form, and is edge restrained asby the clamping action of abacking plate bonded to the diaphragm. In the simplest case, a circulardiaphragm is clamped near its periphery and uniformly loaded across thediaphragm, as 'in the diaphragm of a pressure gage, for example. Thereverse or'obverse surfaces of the diaphragm, or 'both surfaces, cancarry a bridge film pattern bonded thereon. When the diaphragm is ofitself electrically conductive, as when formed from.

bridge pattern can be bonded directly to the diaphragm and the segmentsinsulated from each diaphragm.

other by the In order to more fully describe certain features andadvantages of the invention, consideration will be given to the gagefactors of the film material and to the relationship between the ,gagefactors and bridge output,

'i.e. bridge sensitivity.

The gage factor G of an electroconductive material is defined as theratio ofthe fractional change of resistance R and the fractionalelongation AR AZ 'The output voltage AV expressed as a fraction of theapplied voltage V depends upon the combined 7 ARV of thebridge arms;specifically equals one-quarter of the sum of the values of for the fourbridge arms.

The potential across the output depends on the potential establishedacross the input, and it is thus desirable that the active film segmentscomposing the bridge be of sufiiciently high resistance to permitapplication of a relatively high potential across the input of thebridge without excessive current flow. In typical examples, theresistance R of each active film segment of the bridge is about 100-2000ohms.

The value of the gage factor G as defined by the above equation isdifferent if the direction of current flow is parallel to the strainAl/l than when the elongation is exerted in a direction perpendicularto, i.e. transverse to, the direction of current flow. In other words,rather than a single gage factor G, there are actually two gage factorsinvolved. These gage factors may be represented by the symbols 6,, and GAs will be apparent, in the situation where a bridge arm is subjected tostrain in directions both parallel and perpendicular to the direction ofcurrent flow, then the resulting is thesum of the values that wouldresult from either strain acting separately. Recognition of thisdistinction between the two gage factors G and G is important becauseelectroconductive materials vary considerably as to the values of G andG and unless the relative contributions thereof are taken into accountin orienting the active film segments in relation to the radial andtangential stresses, less than full utilization of the internal changein resistivity and loss in overall sensitivity of the bridge result. Thesignificance of the interrelation of the radial and tangential stressesand the parallel and transverse gage factors G and G, are developed morespecifically hereinafter.

In order to obtain a maximum output per volt input to the bridge, it isdesirable to maximize the value of for each segment. Studies incident tothe present invention indicate that the value of is dependent upon ther/a position and direction of the segments on the diaphragm andalso uponthe gage factors G and 6,, as above indicated. These parametersinfiuence the pattern of thearrangement of the bridge segments in theideal case. However, at least for small diaphragms, where the segmentsare relatively close self-balanced bridge networks, will be apparentfrom the following description, together with the accompanying drawings,wherein like numerals refer to like parts, and wherein:

FIG. 1 is a graphical presentation of the distribution of radial andtangential stresses occurring in a typical edge restrained circulardiaphragm under uniform loading, which graphical presentation serves toshow some of the governing principles and considerations as to locatingthe active film segments on a diaphragm in accordance with the presentinvention;

FIG. 2 is a plan view of the exposed face of a typical bridge patternaccording to the present invention, showing its orientation with respectto the diaphragm on which it is bonded;

FIG. 3 is a view in diametric cross section through a transducerassembly employing a bridge pattern configuration such as shown at FIG.2.

FIGS. 4, 5, 6, 7 and 8 are views similar to that of FIG. 2, illustratingmodified forms of bridge patterns characteristic of the invention;

FIGS. 9, 10 and 11 are cross sectional views similar to the view of FIG.3, showing further variations of transducer arrangements according tothe invention;

FIG. 12 is a view in vertical cross section illustrating a typicalassembly mechanism for fabricating transducer assemblies according tothe invention;

FIG. 13 is a fragmentary view on a somewhat enlarged scale of themechanism shown in FIG. 12, further illustrating the backing plateclamping arrangement thereof, and taken substantially along line 13-13thereof;

FIG. 14 is a further view of a fragmentary nature of the mechanism shownin FIG. 12, showing the relation of elements with the diaphragm andbacking plate assembled; and

FIG. 15 is a view similar to FIG. 14 of a modified form of assemblymechanism, wherein the backing plate and diaphragm are assembled inreverse positions, as compared with the assembly procedure of FIG. 14.

In order to realize the basic principles and advantages of theinvention, an analysis of the forces exerted upon the active filmsegments and the changes in resistance resulting from such forces isnext presented.

In the following analysis, the diaphragm is assumed to be circular, edgerestrained and loaded uniformly across its face to generate compressiveand tensile stresses across the face of the diaphragm. In this respect,and while the following discussion refers to simultaneously occurringcompression in certain regions while tension occurs in other regions, itwill be understood that loading of the diaphragm in the reversedirection is governed by the same principles, except that in suchreverse condition the areas of tension become areas of compression andthe areas of compression become areas of tension.

With the uniform loading of the diaphragm within the range of magnitudesuch that all parts of the diaphragm are displaced linearly, ie. indirect proportion to the applied load, the distribution of stresses onthe diaphragm is given by the following equations:

where S is the radial stress at any point at a distance r measured alongthe radius a from the center; 5, is the tangential stress, i.e., thestress perpendicular to the radius at the above point; W is the load; tis the thickness of the diaphragm; a is the radius of the diaphragm tothe clamped edge; and m is the reciprocal of Poissons ratio (l/m) forthe material of the diaphragm. V

For the value within the brackets in Equation 1, we may Write S,, andfor the value of the bracket in Equation 2, we may write S' Thefollowing table gives the values of S and S, for various values of r/awhere r is the radial position along a radius a at which the stressesare evaluated. The'table gives the values of S, and S, for a silicadiaphragm having an in value of 7.15 and a a sa s p I metallic diaphragmhaving an m value of 3.3, m being the inverse of the Poisson ratio.

++++lllll|l The positive sign indicates that the stress is a tensilestress, and the negative sign that the stress is a compressive stress.

Values for a silica diaphragm from the above table are plotted on FIG.1, in Which the upper plot (designated radial stress) indicates thevalues of S,- for a silica diaphragm of m value of about 7.1 and thelower curve (designated tangential stress) indicates the value of S, forthe same diaphragm as a function of the distance-fromcenter (r/a) atwhich the stresses are evaluated.

The values presented by FIG. 1 are indicative of the actual stresses inany diaphragm because the factor has a constant value K for any givendiaphragm. Also, with diaphragms of various sizes and materials, thefactor 'K has a different magnitude but the shapes of the curvescorresponding to those of FIG. 1 change very little, i.e. the radialstress null zone and tangential stress null zone occur in all instancesat r/a values of about 0.6 and about 0.9, respectively, regardless ofthe diaphragm size and diaphragm material.

For any value of K the radial stress becomes zero at a value of r suchthat r (tn-I- 1 1/2 8 In order to utilize the different magnitudes ofstress occurring in different regions of the diaphragm to obtaln'optimum sensitivity, regions of the diaphragm are selected for adjacentactive segments of the bridge which provide stress factors of oppositesign, i.e. where one segment of the bridge is stressed in tension, aregion is chosen for the one or more active segments connected to itwhich is stressed in compression. Thus, for example, one active segmentis positioned as close to the restrained edge of the diaphragm aspracticable (i.e. near-edge of the diaphragm), and the active segment orsegments connected to it are positioned so as to be as close to thecenter of the diaphragm as practicable (i.e. near-center of thediaphragm) entation of FIG. 1, the active segments aremostadvantageously comprised of a material having a substantialtransverse gage factor G, as well as a parallel gage factor G and atleast one of the active film segments is located to take advantage ofthe tangential gage factor. Thus, for example, those active segmentswhich lie relatively close to the restrained edge of the diaphragm areoriented so that preferably at least about 20% of the total change inthe resistivity of the segments occurs as a result of the relativelylarge radial stress in this area across the segment (noting-the radialstress curve of FIG. 1 at values of r/ a approaching 1.0) which radialstress is responded to in a manner at least primarily determined by thetransverse gage factor G, of the segment. In other words, in certain ofthe bridge pattern designs here presented, the active segment orsegments which lie near the restrained edge of the diaphragm have aconfiguration so that a considerable and preferably predominant portionof their length extends tangentially of, i.e. parallel to, therestrained ments relatively short in bridge pattern design, in that ifunduly long such near-edge segment or segments must be arranged with amultiplicity of reverse bends and must have segment portions positionedrelatively closely to one another, with adverse heating eflects.

With respect to the near-center segment or segments of a bridge pattern,it will be noted from FIG. 1, that the magnitude of the tangentialstress and the magnitude of the radial stress are much more similarbeing substanti'ally equal at the center of the diaphragn'nwiththetangentral stress however being substantially greater in the regionextending from near-center to the radial stress null zone.

For this reason, it has also been found advantageous to I l orient thenear-center segment or segments to extend substantially parallel to therestrained edge, but not critically so, in which location the parallelgage factor of the film material responds to the tangential stress andthe transverse gage factor of the material responds to the radial astress when the film material has a substantial transverse gage factor.

The closer a near-edge active segment is to the restrained edge of thediaphragm, 'the higher will be the value of the radial and tangentialstresses. However,

practically speaking, a near-edge segment can include portions whichhave a radial or chordal as Well as tangential orientation, to increasethe overall length and area of the segment and thus reduce localized,heating. On the other hand, for the near-center segment or segments, thecloser such are located to the center of the diaphragm, the greater thevalue of the radial and tangential stresses. However,'heating effectsand the desirability of having the near-center segments of about the vsame length/width ratio as 1 the near-edge segments introduce compromiseconsiderations so that as a practical matter the near-center segmentsare placed in the re.-

gion where r/a values are about 0.35 to 0.6: As earlier indicated, it isdesirable to not only attain a maximizin of the value but also to obtainactive film segments of sufficient area to distribute the heatingeflect. Accordingly, selectionof the segment orientations, whetherradial, arcuate, chordal, or combinations thereof, will depend upon theG and G, gage factors of the material, the overall length of thesegments desired, the placement of segments to minimize heating, and thecontribution of the r/a placement as reflected by the comparativetangential stress and radial stress involved.

In the specific bridge patterns herein disclosed, both of the near-edgesegments are of relatively the same configuration and are symmetricallyspaced about the diaphragm center. Similarly, the near-center segmentsare in turn of the same configuration relative to one another and aresymmetrically spaced from the center.

The film bridge pattern shown in FIG. 2 comprises an opposed pair ofactive film segments 20 and 22, of equal length and width, andsymmetrically spaced from the center 24 of the diaphragm 26 in a chordalnear-center disposition. The active film segments of the bridge patternshown in FIG. 2 also comprise a second opposed pair of segments 28 and30 which are primarily arcuate and situated in near-edge disposition,i.e. adjacent to the clamped or restrained edge of diaphragm 26, theclamp line being indicated in FIG. 1 at 32. The junction of therespective pairs of opposed bridge film segments 20, 22, 28 and 30 arejoined by output connector segments 34, 36, 38 and 40 which extend fromthe respective juncture areas 34', 36 38 and 40' to the peripheral edge26 of the diaphragm in each instance, and are integrally formed with butconsiderably Wider in dimension than the active film segments 20, 22,23, 30 to provide relatively low resistance. Said output conductorsegments 34, 36, 38, 40 in their peripheral portions are each solderedto a respective output lead 42, 44, 46 and 48, the respective solderarea in each instance being indicated at 50, 52, 54 and 56'.

The clamped or restrained edge 32 of the diaphragm as illustrated atFIG. 2 is established by mounting of the diaphragm 26 on a backing plateS (FIG. 3) by means of an adhesive ring 60 providing a bond between theportions of the diaphragm lying under line 32 and an inset or groove 62provided adjacent to the edge of said backing ring 58. As shown in FIG.3, said backing plate 58 optionally includes a boss or stop portion 58centrally contiguous of diaphragm 26, which stop portion 58' serves tolimit the extent of movement of the diaphragm 26 and prevent accidentalbreakage thereof in the event of application of excessive pressure.

Bonding of the diaphragm 26 and backing plate 58 is preferably but notnecessarily augmented by a ring of encapsulating resin 64 encirclingbacking plate 58 and adhering to it as well as the peripheral area ofdiaphragm 26 lying between the outer edge 66 of the backing plate 58 andthe peripheral edge 26' of the diaphragm 26. Such outer bonding ring 64encapsulates and effectively insulates as well as physically strengthensthe respective connections 59, 52, 54 and 56 between respective outputconductor segments 34, 36, 38, 40 and output leads 42, 44, 46, 48.

In the illustration of the diaphragm provided by FIG. 3

(and also in FIGS. 9-11 discussed below), the thickness dimension of thebridge film pattern is necessarily exaggerated for illustrationpurposes. In actuality, the thickness of the bridge film pattern in atypical transducer assembly is suitably on the order of 100* angstroms.

The bridge film pattern configuration shown at FIG. 2 is suitable foruse where the film material has not only a substantial parallel gagefactor G but also a substantial transverse gage factor 6,, so as topermit the tangential stresses to make a significant contribution to thechange in resistance of the active film segments. Active film segments2%, 22 are of relatively equal length, equally spaced about both sidesbut relatively near the center 24 of the diaphragm, while the activefilm se ments 28, 36' are similarly of relatively'equal length and lieclose to the clamped edge 32 of the diaphragm.

film segments 28, in the pattern shown at FIG. 2 are disposed to lieprimarily quite near the clamped edge 32 of the diaphragm 26, and extendarcuately therealong except for relatively short chordal sections 28',30' connecting the arcuate sections of segments 28 with juncture areas34', 36', 38, 40'.

Relating the bridge pattern configuration shown at FIG. 2 to the stressrelationships graphically presented at FIG. 1, it will be seen that thenear-edge film segments 28, 30, including the short chordal portions 2830 thereof, are of a radial distance from the center 24 so that thesesegments lie entirely in regions of the diaphragm 26 where the r/avalues are greater than As shown by FIG. 1, this corresponds to valuesof r/a of greater than about 0.6, and the placement of said near-edgesegments 23, 30' is such that such lie entirely in the area of diaphragm26 where the r/a ratio is greater than about 0.6. More specifically,juncture areas 34', 36, 38', 40" are placed to fall at points where thevalue of r/a is about 0.7, and the arcuate sections of the seg ments 28are placed so that the center lines thereof fall at an r/a value greaterthan about 0.9, e.g. a value of about 0:95. It will be seen from FIG. 1,that the radial stress factor in and outside of the tangential stressnull zone is quite high and the tangential stress is either about zeroor is of the same sign, i.e. augments or at least does not oppose theradial stress. With the disposition of such arcuate sections of segments28, 30 to be parallel to the restrained edge 32, the parallel gagefactor G,, of the film material is related to the tangential stress, andthe perpendicular gage factor G, of the material is related to theradial stress, with the AR sensitivity primarily responding in a mannerdetermined by the G, of the film material. If the material making up thebridge pattern had no transverse gage factor G it will be observed thatvery little change in resistance of film segments 2%, 39 would occur inresponse to change in stress. By use of a material having a substantialtransverse gage factor, however, and placement of at least the primarypart of the active film segments 28, 30 near the restrained edge of thediaphragm, the high radial stress factor is utilized to good advantage,and tangential stress opposition. or loss is also avoided so thatoptimal sensitivity re sults.

The near-center film segments 20, 22, in the bridge pattern shown inFIG. 2, lie along chords which are geometrically aligned with segmentportions 28', 30. With respect to the desired placement of saidnear-center segments 2%, 22, the closer these are to center 24 of thediaphragm, the greater the negative value of AR/ R (again note FIG. 1).However, it is also important to not place the near-center segments 20,22 too near each other, because of adverse heating effects. For thisreason, the near-center segments 20, 22 are placed to be not less thanabout an r/a value of about 0.35 distance from the center 24 of thediaphragm. With the chordal configuration of the near-center segments20, 22, as shown at'FIG. 2, such lie entirely within a region where thevalue of r/a is substantially less than i.e. less than about 0.6. Inthis area, and again noting FIG. 1, it will be seen that the radialstress factor and tangential stress factor are both negative andtherefore augment one another without certain portions of the segmentsintroducing opposition or loss from the point of View of sensitivity tochange in resistance resulting from changes in stress. Also, withrespect to the configuration of said near-center segments 20, 22, it isto be observedfrom FIG 1 that although the magnitude of the tangentialstress is a greater negative value, the magnitude of both the'tangentialand radial stress are substantial so that While an optimum near-centersegment configuration lies substantially parallel to the restrained edge32 (noting the bridge patterns presented by FIGS. -8 in this respect)such is not necessarily the case; for example the chordal segment 20, 22can provide adequate sensitivity to change in resistance.

FIG. 4 illustrates a slightly modified variation of the bridge filmpattern shown at FIG. 2, in which the chordal section 23a, 30a of thenear-edge segments 28a, 39:: are directed radially of center 24 of thediaphragm 26. This configuration substantially increases the length ofthe arcuate portions of segments 28a, 30a, and also to some extent thelength of radial portions 28a, 30a.

FIG. 5 illustrates a bridge pattern configuration in which the near-edgefilm segments are primarily radially directed, with each such filmsegment having two radially directed segment portions. As shown at FIG.5, the upper near-edge film segment comprises radially directed segmentportions 70 joined by a relatively low resistance connector portion 72,and the lower near-edge film seg ment comprises radially directedportions 74 joined by relatively low resistance connector portion 76.Also, in the bridge configuration shown at FIG. 5, the near-centersegments 78, 80 are of arcuate configuration and because of their closerplacement to center 24 of diaphragm 26 are shorter in length than thecorresponding segments 20, 22 of the bridge configurations shown byFIGS. 2 and 4. The type of bridge film pattern shown in FIG. 5 has itsjuncture areas 34', 36', 38, 40" in the radial stress null zone of thediaphragm 26, and is particularly adapted for use of a bridge materialhaving no substantial transverse gage factor, e.g. Nichrome, in that itsnearedge segments are radially oriented to respond to the high radialstress in the near-edge region of the diaphragm. Also, where adequatesensitivity in resistance can be obtained by comparatively short segmentlengths, the bridge configuration shown at FIG. 5 is advantageous fromthe point of view of the physical separation of each active film segmentor segment portion from the others.

PEG. 6 is a variation of the bridge pattern shown by FIG. 5, in whichthe near-edge active segments 76a and 'Maare made shorter and increasedin number, as compared with segment portions 7t '74 of FIG. 5, suchsegment portions 76a, 74a being respectively connected in series bymeans of relatively low resistance, arcuately extending connectors 72aand 76a. By this variation, the radially extending, near-edge segmentportions 76a, 74a are increased in total effective length, if desired,while still retaining an orientation in the region of the diaphragmhaving an r/a value greater than about 0.6.

FIG. 7 illustrates yet another variation of bridge configurationcharacteristic of the invention, wherein each near-edge segment isformed of a plurality of respective segment portions 82 and 84 formingsmall acute angles with radii of the diaphragm, which chord segmentportions 82, 64 are joined by respective short, arcuately extendingsegment portions 86 and 88 lying nearest the restrained edge ofthediaphragm, and also joined by respective arcuately extending,relatively low resistance connectors 90 and 92 lying relatively near therespective juncture areas .34, -46" and 36', 33'. Also, in keeping withthe greaterefiective length of the near-edge bridge segments 82, 86 and84, 88, thearcuately extending, nearcenter bridge segments 94 and 96 ofthe bridge configuration shown at FIG. 7 are comparatively longer thanthe corresponding near-center segments '78, iii? of the configurationsshown at FIGS. 5 and 6.

FIG. 8 serves to illustrate a further type of variation in bridgepattern configuration,.wherein the juncture areas terminating the activefilm segments in the radial stress null zone are brought to the edge ofthe diaphragm separately. Selecting the configuration of active segmentsof the bridge pattern of FIG. 7 to serve to illustrate this type ofvariation, the bridge pattern shown at FIG. 8 splits the outputconductor segments 34, 36, 38, 40 of the FIG. 7 configuration intorespective output conductor segments 34a and 34b, 36a and 36b, 38a and38b, and 40a and 40b. By this arrangement, the near-edge bridge segments82, 86 connects only to juncture areas 34a and 40b, near-edge bridgesegment 84, 88 connects only to juncture areas 36]) and 38a, near-centerbridge segment 94 connects only to juncture areas 38b and 4%, andnear-center bridge segments 96 connect only to juncture areas 34b and36a. To complete the output connections, and by analogy to the outputconnection of arrangement shown with respect to the bridge pattern ofFIG. 2, the output conductor segments 34a, 34b, 36a, 36b, 38a, 38b, 40aand 40!) areeach soldered to respective output leads 42a, 42b, 44a, 44b,46a, 46b, 43a and 48b, the respective solder area in each instance beingindicated at 66a, 5%, 52a, 52b, 54a, 54b, 56a and 5612.

Should such be desired, the bridge configuration of FIG. 8 enables theuseexternally of the transducer of temperature compensating and trimresistors such as conventionally used in electrically balancing aWheatstone bridge. While it is an advantage and preferable objective ofthe bridge configurations of the present invention to provide that suchare internally resistively balanced, it will be understood that a degreeof external balancing may at times be desired, and FIG. 8 serves to showin this respect that the bridge patterns of the invention readily havethis capability.

FIGS. 9, l0, and 11 illustrate certain typical variations with respectto the make-up of transducer assemblies comprising an edge restraineddiaphragm 26, Le. certain modifications of the transducer assemblyearlier discussed with respect to FIG. 3. Thus, in FIG. 9, thediaphragm-26 with its film pattern 20, 22, 36, 40 can be bonded by adhesive ring 60 and encapsulating ring 64 to a relatively rigid backingplate 56a having a centrally provided bore 100 in communication withpressure tube 102, by means of which fluid of a pressure to be measuredis introduced into the, interspace between diaphragm 26 and backingplate 53% With such arrangement, the transducer becomes a differentialpressure gage, sensitive to the difference in pressures establishedbetween the innerface and outerface of the diaphragm 26.

The transducer construction shown at FIG. 10 shows another variation inbacking plate detail, its backing plate 1 58b being cut away along aninner surface 1634 to provide a larger internal chamber betweendiaphragm 26 and the backing plate 5%, and permit greater flexuraldisplacement of said diaphragm 26.

FIG. ll illustrates a further variation as to backing plateconfiguration of a transducer assembly comprising a diaphragm 26,wherein the backing plate tide is at-.

tached to diaphragm 26 by the encapsulating ring 64, and wherein thebacking plate 58c isof a'thickness substantially equal to the thicknessof diaphragm 26. As will be understood, the forms of backing plates 58band 58c as substantially similar flexural characteristics in both.

The diaphragm can be of metal, such as steel, orcan V be of non-metallicmaterial, such as 'quartz, 'fused silica, glass, plastic or ceramicmaterial, and the backing plate likewise can be of any suitable metallicor non-metallic material with strengthproperties comparable to orgreater" than those of the diaphragm.

A highly useful application of the invention is in connection withminiaturized transducers, with the bridge film pattern applied to adiaphragm of insulating material,

preferably silica. The silica diaphragm is considered particularlyadvantageous by virtue of, its inherently good 13 temperature stabilityand good physical characteristics, with low mechanical hysteresis, withsmall variation of modulus of elasticity which change in temperature,and with a low coefficient of expansion.

With respect to the bridge pattern, such is bonded on the surface of thediaphragm either by glue or other insulating bonding agent, in the caseof metallic diaphragms, or directly on the diaphragm, in the case ofelectrically non-conductive diaphragm materials. The deposition of thebridge film material on the diaphragm or, on an insulating layer bondingsame to the diaphragm, can be by any of several well-known techniques,and the bridge pattern can be developed by any of several well-knowncircuit methods as, for example, by painting, drawing, silk-screeningand photo-engraving. Various techniques for such purpose have beendeveloped, as indicated; see, for example, National Bureau of StandardsCircular 468, entitled Printed Circuit Techniques, National Bureau ofStandards Project 06021l-3583, and National Bureau of Standards Report5139. See also Preliminary Survey of Electrical Strain Characteristicsof Evaporation Films, by Krusky and Parker, February 1957, published bythe Office of Scientific Publications, National Bureau of Standards. Seealso British Patent 689,785.

As for the composition of the material from which the bridge filmpattern is formed, such is to be electroconductive with substantialbut'irelatively low order resistance (e.g. on the order of 100-2000ohmsper active segment), and is preferably a semi-conductive materialexhibiting a substantial transverse gage factor as well as a substantialparallel gage factor, i.e. a'material such as silicon or germaniumalloys, and such as certain metallic resinates. As will be understood,many electroconductive materials compositions has a substantialtransverse gage factor. The gage factors characteristic of any givenelectroconductive material can be readily ascertained by test. However,by way of certain typical examples, it was found that a film of an alloyof 25% Si-75% Cr on glass exhibited a Cr, of 2.1 and a G, of 1.3. A filmof an alloy of 75% Si-25% Cr on glass demonstrated a G of 1.5 and a G,of .54. Some precious metal resinates have proven to be quitesatisfactory for purposes of being utilized as the film materialaccording to the present invention; for example palladium resinatemarketed under the proprietary term Liquid Bright Palladium #4334 byHanovia Liquid Gold Division of Engelhard Industries, exhibited aparallel gage factor of about 2.0 and a transverse gage factor of about0.83. Metallic palladium evaporated onto silicone resin demonstrated a Gof 0.84 and a G, of 1.2.

As shown by certain of the above examples it is a characteristicproperty of certain electroconductive materials that an inverse relationexists between the parallel gage factor G and the transverse gage factorG i.e. the G of the material is a positive factor and the G, of thematerial a negative factor. With such a material, placement of thenear-edge active segments in the region between the radial stress nullzone and the tangential stress null zone results in the radial stressresponse in the nearedge augmenting the tangential stress responsethereof, in that while the stress factors are of opposite sign in thisarea of (cf. FIG. 1) the gage factors are also of opposite sign with theresult that the change in resistance of the segment with change instress is relatively increased.

As will also be understood, certain adaptations of the principles of theinvention can employ only part of the features thereof. Thus, when thefilm material selected for 'a particular transducer design has nosubstantial transverse gage factor, design advantages still pertain tothe orientation of the active segment juncture areas at about the radialstress null zone with one or more segments near-center and one or moresegments near-edge of the diaphragm, but without especial orientation toutilize segment layout to provide substantial cross segment stresses(such as in the bridge pattern presented by FIGS. 5 and 6 for example).In these types of bridge pattern arrangements, for example, it will beunderstood that the bridge pattern material can be any electroconductivematerial with a substantial parallel gage factor, such as Nichrome,manganin or cons-tantin, or can be carbonloaded paints orelectroconductive plastic tape.

In laying the bridge material on one or both sides of the diaphragm, ithas been found preferable to use a vacuum vapor deposit technique, sincethe resulting film is quite uniform in thickness throughout andtemperature coefiicient characteristics are also quite uniform in allportions of the film.

Any suitable technique can be used for vacuum deposition of the film ofelectroconductive material onto the diaphragm, such as disclosed in thetext entitled Vacuum Deposition of Thin Films, by L. Holland, publ. byWiley and Sons (1958), for example.

The thickness of the film can suitably be about 500 Angstrom units, forexample.

With such electr-oconductive film coating formed on the surface of thediaphragm, the bridge film pattern can be developed by any of severalsuitable means, such as by a photo-engraving process wherein the film isfirst coated with a photo resist, then irradiated with visible orultra-violet light from the side upon which the pattern is to bedeveloped, through a positive mask of the pattern to be produced on thediaphragm. Such procedure irradiates all portions of the photo resist inthe pattern. The exposed diaphragm film is then developed by washing inwater or other solution to remove the unexposed photo resist, leavingthe resist in the form of the desired pattern on the surface of thediaphragm.

In some instances, informing the pattern in the deposited film material,the film material can prove rather difficult to remove by conventionalelectrolytic etching.

In such situation, another suitable method of forming the film patternis that of stylus etching. In this procedure, the film material isconnected to the. positive side of a battery, and a porous stylus isused, such as for example a chisel-end wood stylus saturated with anelectrolyte, with the stylus connected to the negative pole of thebattery. The stylus is simply guided over the film material not coatedwith photo resist to form the pattern by removal of the unwantedmaterial. rAlternately, with respect to the pattern formation, a clothsaturated with an electrolyte may be stretched over and spaced somewhatfrom the film material carrying developed resist. With the film materialconnected to the positive pole of a battery and With a wire rodconnected to the negative pole of the battery, the wire rod is rolledacross the cloth and the exposed portions of the film are removed. Anysuitable electrolyte .may be employed. For example, when the filmmaterial is a Si-Cr alloy, a dilute solution of NaOH suffices.

Transducers according to the present invention can be assembled with aninternal pressure which is substantially atmospheric, orsuperatmospheric, as desired, or can be assembled to that the internalchamber pressure is substantially a vacuum.

Typical assembly techniques for transducers according to the presentinvention, will be considered in connection with FIGS. 1215. As shown inFIG. 12, the assembly equipment can comprise a base supporting, as bylegs 112, a support plate 114 having a cut away portion 116 in its upperface to receive diaphragm 26 after the bridge pattern has been formedthereon. Said support plate 114 is suitably heated in the area of thediaphragm plate, as by an electric heating coil, schematically indicatedat 118. Upstanding from support plate 114 are a plurality of guide rods120 which serve to maintain a reciprocable slide plate 122 parallel tothe face of support plate 114. Said slide plate 122 is suitably raisedand lowered by means of a press rod 124 threaded therein and passingthrough stuifing box 126 in cover 128 which in turn attached as by bolts130- to base 119. Cover seals 132 are also provided between cover 128and base 110, and tube 134 permits the pressure inside the cover to bemaintained at any desired value while the transducer is being formed. Ifa vacuum is desired, for example, then the interior of the assemblyequipment is maintained evacuated during the assembly procedure.

Slide plate 122 is circularly recessed as at 136 (FIG. 13) to receivethe backing plate 28, and a slide block 138 with an adjustment bolt 140are provided to clamp the backing plate 28 in proper position in slideplate 122.

With the diaphragm 26 and backing plate 58 in proper positions onrespective support plates 114 and slide plate 122, the annular groove 62of the backing plate is filled with a preformed adhesive ring 60, theslide plate 122 is placed on guide rods 120, the cover installed, andthe desired assembly pressure is established. Then, diaphragm 26 havingbeen placed on and heated by the heating means 118 in the meanwhile, theslide plate 122 is moved down under slight pressure so that firm contactis maintained between diaphragm 26 and backing plate 28 while theadhesive'ring 60 in groove 62 sets (cf. FIG. 14). The assembleddiaphragm and backing plate are then removed from the assemblyequipment, the output leads are soldered to the output connectorsegments (eg in FIG. 2), and the encapsulating ring 64 is applied andcured to complete the transducer assembly.

FIG. 15 illustrates a variation in assembly procedure, suitable for usewhen the chamber between the diaphragm and the backing plate is notvacuumized. This assembly equipment as shown in FIG. 15, is quitesimilar to but constructionally simpler than that of FIGS. l2l4. Backingplate 58 is supported on a smooth base plate 114a, with the diaphragm 26placed thereon after a ring of preformed thermosetting adhesive 60 isplaced in groove 62. Then, a smooth surface slide plate 122a, suitablyheated as by the electric heating coil 118a, is brought down in pressurecontact with the diaphragm 26 and maintained in such position until thering 60 sets.

From the foregoing discussion of the basic principles governing thepresent invention, as well as the typical embodiments thereof presented,various other modifications, adaptations and features thereof will occurto those skilled in the art to which the invention is addressed, Withinthe scope of the following claims.

What is claimed is:

1. A pressure responsive device comprising an edge restrained diaphragmhaving an integral bridge pattern with a plurality of active segmentsinterconnected at juncture areas in turn having relatively lowresistance conductor segments extending beyond the restrained edge ofthe diaphragm; said juncture areas lying substantially in the radialstress null zone of the diaphragm, with one active segment connected toeach juncture area disposed nearcenter from said radial stress null zoneand the other active segment connected thereto disposed near-edge fromsaid radial null zone. u

2. A pressure responsive device according to claim'l,

wherein a major part of the active segment disposed out side of saidradial stress null zone is disposed in the area of and outside thetangential stress null zone of said diaphragm.

3. A pressure responsive device according to claim 1, wherein saidbridge pattern is composed of a material having .a substantialtransverse gage factor as well as a substantial parallel gage factor;said near-edge active segment having a substantial part thereof disposedoutside of the tangential stress null zone of the diaphragm andextending parallel to the restrained edge thereof, so that the bridgematerial in substantial part responds to radialstress in relation to itstransverse gage factor and in substantial 'part responds to tangentialstress in relation to its parallel gage factor, with such responseaugmenting each other.

4. A pressure responsive devirze according to claim 1,

16 wherein said bridge pattern is composed of a thin, integrallydeposited film of elegitroconductive material.

5. A pressure responsive device according to claim 1, wherein saidbridge pattern is composed of a thin, integrally formed film ofelectroconductive material having a substantial transverse gage factoras well as a substantial parallel gage factor.

6. A pressure responsive device according to claim 5, wherein said filmpattern is formed of an electroconductive material having a substantialtransverse gage factor, selected from the group consisting ofsilicon-chrome alloys and metallic resinates.

7. A pressure responsive device according to claim 1, wherein saiddiaphragm is non-metallic and electrically non-conductive.

8. A pressure responsive device according to claim 7, wherein saiddiaphragm is fused silica.

9. A pressure responsive device according to claim 1, wherein saiddiaphragm is metallic and the bridge pattern segments are electricallyinsulated therefrom.

10. A pressure responsive device comprising a diaphragm having anintegral bridge pattern bonded thereto, said pridge pattern arrangementcomprising at least one active segment near the center of the diaphragm,substantially entirely in the region thereof where the distance/ radiusratio is from about 0.35 to about 0.6, and at least one other activesegment disposed substantially entirely in the region where thedistance/radius ratio is at least about.0.7.

11. A pressure responsive device comprising a diaphragm having anintegral bridge pattern bonded thereto, said bridge pattern arrangementcomprising at least one active segment near the center of the diaphragmsubstantially entirely in the region thereof where the distance/ radiusratio is from about 0.35 to about 0.60, and at least one other activesegment disposed nearthe edge of said diaphragm, substantially entirelyin the region where the j distance/ radius ratio is at least about 0.7,such latter active segment being predominantly in and outside of theregion of said diaphragm where the distance/radiusratio is about 0.9.

12. A pressure responsivedevice according to claim 11, wherein saidbridge pattern is composed of an electroconductive material having asubstantial transverse gage factor as well as a substantial parallelgage factor.

13. A pressure responsive device according to claim 12, wherein saiddiaphragm is fused silica.

14. A pressure responsive deviceaccording to claim 13, wherein saidelectroconductive material is an integrally deposited film ofsemi-conductor material.

15. In a pressure responsive device comprising a diaphragm having bondedthereto astrain sensitive bridge pattern with active segments consistingof an integrally formed electroconductive material having a substantialtransverse gage factor as Well as a longitudinal gage face tor, saidbridge pattern having active segments arranged on said diaphragm to besubstantially responsive to strain both perpendicular and parallel tothe direction of current flow therein.

16. A pressure responsive device .according to claim 15, wherein atleast one of said bridge pattern active segm nts is arranged to providethat at least 20% of the total change of resistance thereof occurs fromresponse to strain per pendicular to the direction of current flow.

17. A pressure responsive device according to claim 15, wherein thebridge pattern is comprised of a vacuum deposited film ofelectroconductive material having a substantial transverse gage factor.V

18. A pressure responsive device according to claim 17,

wherein said film pattern is formed of an electroconductive materialhaving a substantial transverse gage factor, selected from the groupconsisting of silicon-chrome alloys and metallic resinates.

19. A pressure responsive device according to claim I 15, wherein saiddiaphragm is a fused silica wafer.

20. In a wafer type pressure responsive device comprising an edgeclamped diaphragm with an integral film pattern bonded to said diaphragmedge-to-edge and in essentially quadrant arrangement, said film patternhaving two diametrically opposite active film segments disposedsymmetrically near the center of said diaphragm, and two otherdiametrically opposite active film segments disposed near the clampededge of said diaphragm, said active film segments terminating injuncture areas substantially at the radial stress null zone of thediaphragm, the thickness of all such active film segments beingsubstantially the same and the length/width ratio of each film segmentbeing substantially equal to the length/width ratio of the other activefilm segments so as to be internally balanced resistively and so as tobe internally temperature compcnsated, and all of such resistor filmsegments being spaced substantially one from another so as to minimizeheating effects.

21. A pressure responsive device according to claim 20, wherein saidactive film segments are composed of an electroconductive materialhaving a substantial transverse gage factor as well as a parallel gagefactor, and the active film segments near the center of the diaphragmextend at least primarily circumferentially thereof to longitudinallyreceive tangential diaphragm stress and transversely receive radialdiaphragm stress, the active film segments situated near the clampededge of the diaphragm being arranged in a pattern with substantialcomponents thereof extending both tangentially and radially to besensitive to both tangential and radial stress.

22. A pressure responsive device according to claim 21, wherein saidfilm pattern is formed of an electroconductive material having asubstantial transverse gage factor, selected from the group consistingof silicon-chrome alloys and metallic resinates.

23. A pressure responsive device according to claim 20, wherein saiddiaphragm is a fused silica wafer.

24. A wafer type pressure responsive assembly, comprising a pressuresensitive diaphragm, and an electro-conductive film pattern on saiddiaphram with at least one active segment situated near-center of saiddiaphragm and at least one active segment situated near-edge of saiddiaphragm and with relatively low resistance conductor segments integralwith and extending from juncture areas as the ends of said activesegments to the periphery of said diaphagm, said assembly furthercomprising a backing plate annularly bonded to said diaphragm near theperiphery of said diaphragm, said backing plate being overlapped byportions of said conductor film segments.

25. An assembly according to claim 24, wherein said backing plate issubstantially more rigid than said diaphragm.

26. An assembly according to claim 24, wherein said diaphragm and saidbacking plate are formed of the same material.

27. An assembly according to claim 24, wherein said diaphragm and saidbacking plate are of substantially the same thickness and consequentlyhave similar flexural characteristics, the fiexure of the backing platethus augmenting the pressure responsive flexural characteristics of saiddiaphragm.

28. An assembly according to claim 27, wherein said diaphragm and saidbacking plate are fused silica.

29. An assembly according to claim 27, wherein said diaphragm and saidbacking plate are metal.

30. A wafer type pressure responsive assembly, comprising a pressuresensitive diaphragm, and an integrally formed electroconductive filmpattern on said diaphragm with at least one active segment situatednear-center of said diaphragm and at least one active segment situatednear-edge of said diaphragm, and with relatively low resistanceconduct-or segments integral with and extending from juncture areas atthe ends of said active segments to the periphery of said diaphragm,said assembly further comprisinga backing plate annularly with saidconductor film segments overlapping said backing plate, and conductoroutput leads connected to said output conductor segments externally ofsaid backing plate at about the peripheral edges of said diaphragm.

31. A wafer type pressure responsive assembly, comprising a pressuresensitive diaphragm, and an electroconductive film pattern on saiddiaphragm, said film pattern comprising at least one active segmentsituated nearcenter of said diaphragm and at least one active segmentsituated near-edge of said diaphragm, such pattern further comprisingrelatively low resistance conduct-or segments integral with andextending from juncture areas at the ends of said active segments to theperiphery of said diaphragm, a backing plate bonded to said diaphragmnear the edge thereof and contacting portions of said conductor filmsegments, conductor output leads connected to said output conductorsegments externally of said backing plate at about the peripheral edgesof said diaphragm, and bonding means between the periphery of saiddiaphragm and the outer portion of said backing plate retaining the sametogether and encapsulating the connections between said film conductorsegments and said output leads.

32. An assembly according totclaim 31, wherein said backing plate issubstantially more rigid than said diaphragm.

33. An assembly according to claim 31, wherein said diaphragm and saidbacking plate are formed of the same material.

34. An assembly according to claim 31, wherein said diaphragm and saidbacking plate are of substantially the same thickness and have similarflexural characteristics, the fiexure of the backing plate thusaugmenting the pressure responsive flexural characteristics of saiddia-.

phragm.

35. An assembly according to claim 34, wherein said diaphragm and saidbacking plate are fused silica.

36. An assembly according to claim 34, wherein said diaphragm and saidbacking plate are thin metal.

37. A wafer type pressure responsive assembly, comprising a pressuresensitive diaphragm, and an electroconductive bridge pattern on saiddiaphragm, said bridge pattern comprising an integral film with at leastone active segment situated near-center of said diaphragm and at leastone active film segment situated near-edge of said diaphragm, and withrelatively low resistance conductor segments integrally extending fromabout the radial stress null zone of said diaphragm to the peripherythereof, said assembly further comprising a backing plate bonded to saiddiaphragm and to said conductor segments near the outer edge of saiddiaphragm.

38. A Wafer type pressure responsive assembly, comprising a pressuresensitive diaphragm, and an electroconductive bridge pattern on saiddiaphragm, said bridge pattern comprising an integral film with at leastone active segment situated near-center of said diaphragm and at leastone active film segment situated near-edge of said diaphragm, and withrelatively low resistance conductor segments integrally extending fromabout the radial stress null zone of said diaphragm to the peripherythereof, a backing plate bonded to said diaphragm and said conductorsegments near the outer extent thereof, conductor output leads connectedto said output conductor segments externally of said backing plate atabout the peripheral edge of said diaphragm, and thermosetting bondingmeans between the periphery of said diaphragm and the outer portion ofsaid backing plate retaining the same together and encapsulating theconnections between said conductor segments and said output leads.

39. A strain sensitive Wafer type pressure transducer assembly,comprising a flexible diaphragm, and an integrally deposited filmpattern on at least one surface of said diaphragm, said film patterncomprising two oppositely disposed active film segments situated withinthe radial stress null zone of said diaphragm and two opposite'lydisposed active film segments situated at least primarily in the area ofthe tangential stress null zone of said diaphragm, such film patternfurther comprising relatively low resistance output conductor filmsegments connecting with said active film segments in about the saidradial stress null zone and extending outwardly therefrom to theperiphery of said diaphragm, a backing plate bonded to said diaphragmand said conductor film segments near the outer extent thereof,conductor out-put leads connected to said output conductor seg mentsexternally of said backing plate at about the peripheral edges of saiddiaphragm, and thermosetting bonding means between the periphery of saiddiaphragm and the outer portion of said backing plate retaining the sametogether and encapsulating the connections between said conductor filmsegments and said output leads.

40. In a wafer type pressure responsive device comprising an edgeclamped diaphragm with an integrally formed film patternbonded to saiddiaphragm edge-toedge and in essentially quadrant arrangement said filmpattern having at least one active segment disposed inside the radialstress null zone of said diaphragm and at least one active film segmentdisposed outside the radial stress null zone of said diaphragm, thethickness and length/width ratio of the active film segments beingsubstantially equal, and the active film segments being spacedsubstantially one from another so as to minimize heating effects. s

41. A transducer comprising a circular flexible diaphragm, means toclamp said diaphragm near its peripheral. edge, a bridge patternincluding two pairs of active resistor segments bonded to saiddiaphragm, the resistor segments of a first pair being positioned on thesurface of said diaphragm near the clamped edge thereof, the net stressin the diaphragm at said first pair of resistor segments upon impositionof a uniform load being of net positive value, said first pair ofresistorsegments being symmetrically and oppositely arranged on thediaphragm, the resistor segments of the second pair of segments beingpositioned adjacent to the center of the diaphragm, the net stress inthe diaphragm in the area of said second pair .of resistor segmentsbeing of negative value, said second pair of resistortsegments alsobeing symmetrically and oppositely arranged on said diaphragm, saidbridge pattern further comprising junction areas interconnectingadjacent resistor segment ends, said juncture areas at least in partbeing in a region of the diaphragm where the factor No references cited.

1. A PRESSURE RESPONSIVE DEVICE COMPRISING AN EDGE RESTRAINED DIAPHRAGMHAVING AN INTEGRAL BRIDGE PATTERN WITH A PLURALITY OF ACTIVE SEGMENTSINTERCONNECTED AT JUNCTURE AREAS IN TURN HAVING RELATIVELY LOWRESISTANCE CONDUCTOR SEGMENTS EXTENDING BEYOND THE RESTRAINED EDGE OFTHE DIAPHRAGM; SAID JUNCTURE AREAS LYING SUBSTANTIALLY IN THE RADIALSTRESS NULL ZONE OF THE DIAPHRAGM, WITH ONE ACTIVE SEGMENT CONNECTED TOEACH JUNCTURE AREA DISPOSED NEARCENTER FROM SAID RADIAL STRESS NULL ZONEAND THE OTHER ACTIVE SEGMENT CONNECTED THERETO DISPOSED NEAR-EDGE FROMSAID RADIAL NULL ZONE.